Graphite chamber manufacturing process

ABSTRACT

A method for manufacturing a filament wound chamber combining circular and helical winging configurations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to rocket motor chambers. More particularly, thisinvention relates to a method for manufacturing rocket motor chambers.Still more particularly, but without limitation thereto, this inventionrelates to a process for manufacturing graphite chambers.

2. Description of the Prior Art

Various techniques have been attempted in the prior art to develop achamber which balanced the need for maximum strength and minimum weight.An example of one such measure is the utilization of graphite-epoxycomposite materials.

Recent studies indicate that the pattern of winding composite materialshas an effect upon the strength of the chamber. This invention utilizesa winding pattern which improves strength and in doing so, eliminatesthe need for reinforcement wafers, thereby minimizing the overall weightof the chamber.

SUMMARY OF THE INVENTION

An object of the present invention is to develop a rocket motor chamberwhich is lightweight and strong.

A further object of the present invention is to develop a chamberpressure vessel with sufficient strength so as to eliminate the need forreinforcement wafers, which will thereby reduce the chamber's overallweight and the risk of voids.

These and other objects have been demonstrated by the present inventionwherein a chamber pressure vessel is formed over internal insulation bywrapping with graphite-epoxy composite material in such a manner so asto incorporate both circular and helical configurations in the windingpattern.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in further detail with reference to theaccompanying drawings wherein:

FIG. 1 is a cross sectional view of the rocket chamber taken along thelongitudinal axis;

FIG. 2 is an enlarged detail view of the junction between the aft andthe forward ends of the chamber; and

FIG. 3 is a schematic representation illustrating the winding pattern ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates the assembled filament wound chamber 10, having apressure vessel 12, a forward end 14 and an aft end 16.

The forward end 14 consists mainly of a forward bearing ring 18 and aforward insulator 20, which is bonded to the internal surface of thepressure vessel 12. The aft end 16 consists of an aft bearing ring 22and an aft insulator 24 which, as the forward insulator, is also bondedto the internal surface of the pressure vessel 12. FIG. 2 illustratesthe junction where the forward insulator 20 and the aft insulator 24meet. The junction is reinforced by a splice strip 26.

FIG. 1 further illustrates the forward skirt 28 and the aft skirt 30. Aportion of the area where the skirts 28 and 30 and the pressure vessel12 meet, is filled in by means of a forward Y-joint filler 32 and an aftY-joint filler 34. The Y-joint fillers are preferably of a rubber suchas styrene butadiene.

The invention is a method of winding the pressure vessel 12. Thisprocess begins with the assembly of a net metal mandrel, not shown,which defines the internal cavity into which the propellant grain iseventually loaded. Upon the net mandrel is placed the forward 20 and aft24 insulators, which are respectively attached to the forward 18 and aft22 bearing rings. These two insulators are then joined by bonding themwith the splice strip 26 as is shown in FIG. 2. The bonding process isaccomplished by vulcanization using an uncured rubber splice strip. Oncethe bonding is complete, the outer contour of the insulators 20 and 24,now joined, provides the winding surface upon which the chamber iswound.

FIG. 3 shows the method of winding the pressure vessel 12, andsubsequently the forward and aft skirts 28 and 30, respectively.

The pressure vessel 12 is wrapped with a graphite-epoxy compositematerial, more specifically carbon fiber which has been wet wound withan amine cured epoxy resin. The wrapping process utilizes both circularand helical patterns. The initial layer 36 which is directly adjacent tothe insulators 20 and 24, is helical, as is the final layer 38. In theprocess of wrapping, four other layers are also of the helicalconfiguration, namely 40, 42, 44 and 46. The angle of wrapping thehelical layers varies from about 71.8 degrees at the forward end toabout 71.2 degrees at the aft end. The angles, θ_(A) and θ_(B), as shownin FIG. 1, are measured from the vertical datum lines 48 and 50.

Alternating with the helical patterned layers 36, 38, 40, 42, 44 and 46are circular patterned layers 52, 54, 56, 58 and 60. While the helicallayers are made by a single pass of the material, the circular layersare made by several passes around the vessel 12, as is shown in FIG. 3.For example, circular layer 52 has approximately four passes, whilecircular layer 60 has about two.

Therefore, the pressure vessel 12 is formed by helical layersalternating with circular layers, the former being formed by a singlepass and the latter being formed by several passes. One of the mostcritical considerations in achieving optimum strength is to start andend with layers of helical configuration, as is shown by layers 36 and38.

When application of the graphite-epoxy composite material is complete,forward and aft skirt bond elastomers 62 and 64 and the forward and aftY-joint fillers 32 and 34 are placed as shown in FIG. 3. The elastomersare preferably of a rubber such as acrylonitrile butadiene.

The forward skirt 28 and the aft skirt 30 are prepared in a mannersimilar to that of the pressure vessel 12 in that alternating helicaland circular winding configurations are utilized.

For illustrative purposes, only the winding pattern for the forwardskirt 28 is described in detail. The initial layer 66 is glass cloth.This is followed by alternating circular layers of graphite-epoxycomposite material, more specifically wet wound carbon fibers, withlayers of precut parallel fiber broadgoods which are preimpregnated withan epoxy resin.

Layer 66 is followed by layers 68 and 70 which are both broadgoodslayers. However, while layer 68 is laid out at a 45 degree angle, layer70 is laid out at a 0 degree angle, both angles being measured from thedatum line 48. The next layer 72 is formed by making two circular passeswith wet wound carbon fibers. The winding pattern of the forward skirt28 continues in the same manner: 45 degree broadgoods layer, 0 degreebroadgoods layer and circular wet wound carbon fiber layer (two passes).In that manner layers 74, 76, 78 and 80 are 45 degree broadgoods, layers82, 84, 86 and 88 are 0 degree broadgoods and layers 90, 92, 94 and 96are wet wound carbon fibers, with layer 96 being the final layer of theforward skirt 28.

The aft skirt 30 is prepared in a manner similar to that of the forwardskirt 28. Starting with an initial layer of glass cloth 98, the samepattern of 45 degree broadgoods, 0 degree broadgoods and circular wetwound carbon fiber (two passes) is followed. The only difference betweenthe winding pattern of the forward skirt 28 and the aft skirt 30 is thatthe aft skirt has an extra 45 degree layer 100, 0 degree layer 102 andfinal circular layer (two passes) 104, as is shown in FIG. 3.

Care is taken in laying out the skirts, that the forward skirt 28 doesnot extend internally beyond the aft end of the forward skirt bondelastomer 62. Likewise, the aft skirt 30 should not extend beyond theforward end of the aft skirt bond elastomer 64. The external ends ofskirts 28 and 30 may be cut to size so as not to extend over the forwardend of elastomer 62 and the aft end of elastomer 64.

Upon completion of wrapping the pressure vessel 12 and the skirts 28 and30, the chamber is wrapped with a teflon coated glass cloth and thencured in a hot air oven.

This invention had been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. A method of manufacturing a chamber pressurevessel wherein a chamber having a forward end, an aft end, forwardinsulation and aft insulation, is wrapped with graphite-epoxy compositematerial, alternating circular and helical winding configurations,beginning and ending with said helical configuration.
 2. The method ofclaim 1 wherein said helical winding configuration at said forward endis at an 71.8 degree angle.
 3. The method of claim 1 wherein saidhelical winding configuration at said aft end is at an 71.2 degreeangle.